This invention relates to an improvement in soils. Particularly it relates to soil amendment matters effective for improving soils which suffer from injuries due to continuous cropping which means herein repeated cultivations of the same crop on the same field.
Recently, in most of the districts where leafy vegetables or fruit vegetables are produced, continuous cropping of specified crops have often been carried out from necessity of management, and as the number of years of continuous cropping increases, the injuries due to continuous cropping occur frequently, and this has been raising a serious problem in cultivation.
Representative injuries due to continuous cropping are Fusarium-wilt of watermelon, melon, cucumber or the like, damping off of tomato, pepper or the like, other wilts of Japanese radish, strawberry or the like, clubroot of Chinese cabbage, turnip, salting greens, cabbage or the like. Most of pathogenic microorganisms causing these diseases belong to fungi such as Fusarium, Plasmodiophora, etc.
As for the measures for preventing the injuries due to continuous cropping, treatments such as spray of fungicides, fumigation, etc. have generally been carried out. However, these methods have various drawbacks in that chemicals used neither selectively inhibit nor kill pathogenic fungi alone, but they act inhibitorily also on non-pathogenic microorganisms including essential ones e.g. nitrifiers, ammonifiers, or when pathogenic microorganisms again invade soils which have been sterile after the treatments, they propagate easily, resulting contrarily in more violent damages, and moreover, a certain period of time is often required till the chemicals after the treatments vanish and become harmless to crops or humans and domestic animals.
Thus, the present invention is to provide a method for preventing injuries due to continuous cropping, by suppressing pathogenic fungi without inhibiting essential microorganisms, and inflicting no damages on crops or humans and domestic animals. In the studies for attaining the object, the present inventors have found that when 2-oxo-4-methyl-6-ureidohexahydropyrimidine (which will be hereinafter referred to as "OMUP") is applied to soils, the injuries due to continuous cropping are sometimes alleviated. However, the effect attained by such a method is unstable and it generally takes considerable days till the actual effect is developed. The injuries of crops due to continuous cropping generally occur as a result of invasion of pathogenic fungi at a certain limited period of growth of crops (very often at the initial period of growth); hence it is important for preventing the injuries to protect the roots of crops from pathogenic fungi for a definite period during the growth. Thus, a soil amendment matter is desired which does not require a long time in developing the effect of preventing the injuries due to continuous cropping; brings about a reliable preventing effect; and makes it easy to apply the matter at an adequate time and effectively in accordance with cultivation plan. In this respect, the object cannot be attained by a single application of OMUP, and advent of a more effective and more reliable matter which makes it possible to prevent the injuries due to continuous cropping has been desired As a result, the present inventors have found that a product of a cultivation treatment carried out under aerobic conditions using OMUP as main organic nutrient is effective, and further, a product obtained by making OMUP coexistent with the above product is more effective.